1. Field of the Invention
The present invention is in the field of magnetic tape playback systems and, in particular, relates to a system in which a real-time display can be produced from a high-speed playback of a segment of a magnetic tape.
2. Description of the Prior Art
Considerable progress has been made in the last decade in recording and analyzing electrocardial signal obtained from a patient. In the Holter technique, the patient is provided with a small portable tape recorder on which his electrocardial signals are recorded over an extended period of time as the patient goes about his daily activities. It is now possible to record such signals continuously over intervals up to 24 hours on a single tape. This is accomplished by recording the tape at speeds as low as 1/16 inch per second. A recorder for this purpose is described in the copending application "Recorder for Cardiac Signals", Ser. No. 773,618, filed Mar. 2, 1977, and assigned to the assignee of the present invention.
It would be prohibitively expensive to examine an entire 24-hour recording at real-time speeds. Such tapes are normally scanned at a higher speed on specialized scanners, such as that described in U.S. Pat. No. 4,006,737 for Electrocardiographic Computer, issued Feb. 8, 1977 to Cherry and assigned to the assignee of the present invention. It is known to provide the playback scanner with the capability of displaying the signal at various speeds, but such scanners lack the ability to "freeze" the displayed action for extended study.
The electrocardial signals have significant frequency components in the lower audio range, and the design of playback heads capable of satisfactory operation at both high-speed and real-time playback speeds is difficult.
Thus, it became clear that a need existed for a playback and display system which would permit a segment of the magnetic tape to be "frozen" on the display and to be advanced and reversed at various speeds. From the standpoint of playback head efficiency, it also is desirable that the playback tape speed be a constant speed considerably higher than the real-time speed at which the tape was recorded.